Unexpected renewal costs
Some commercial antivirus software end-user license agreements include a clause that the subscription will be automatically renewed, and the purchaser's credit card automatically billed, at the renewal time without explicit approval. For example, McAfee requires users to unsubscribe at least 60 days before the expiration of the present subscription while BitDefender sends notifications to unsubscribe 30 days before the renewal. Norton Antivirus also renews subscriptions automatically by default.
Rogue security applications
Some antivirus programs are actually malware masquerading as antivirus software, such as WinFixer and MS Antivirus. A recent surge in such software has deceived more than a million Microsoft Windows internet users and prompted the FTC to initiate court proceedings.
Problems caused by false positives
A false positive is identifying a file as a virus when it is not a virus. If an antivirus program is configured to immediately delete or quarantine infected files (or does this by default), false positives in essential files can render the operating system or some applications unusable. In one case, a faulty virus signature issued bySymantec mistakenly removed essential operating system files, leaving thousands of PCs unable to boot. In another case, the executable file required by Pegasus Mail was falsely detected by Norton AntiVirus as being a Trojan and it was automatically removed, preventing Pegasus Mail from running.
Running multiple antivirus programs concurrently can degrade performance and create conflicts.
It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers.Active antivirus protection may partially or completely prevent the installation of a major update.
Studies in December 2007 have shown that the effectiveness of antivirus software has decreased in recent years, particularly against unknown or zero day attacks. The German computer magazine c't found that detection rates for these threats had dropped from 40-50% in 2006 to 20-30% in 2007. At that time, the only exception was the NOD32 antivirus, which managed a detection rate of 68 percent.
The problem is magnified by the changing intent of virus authors. Some years ago it was obvious when a virus infection was present. The viruses of the day, written by amateurs, exhibited destructive behavior or pop-ups. Modern viruses are often written by professionals, financed by criminal organizations.
Traditional antivirus software solutions run virus scanners on schedule, on demand and some run scans in real time. If a virus or malware is located the suspect file is usually placed into a quarantine to terminate its chances of disrupting the system. Traditional antivirus solutions scan and compare against a publicised and regularly updated dictionary of malware otherwise known as a blacklist. Some antivirus solutions have additional options that employ an heuristic engine which further examines the file to see if it is behaving in a similar manner to previous examples of malware. A new technology utilized by a few antivirus solutions is whitelisting, this technology first checks if the file is trusted and only questioning those that are not.
Independent testing on all the major virus scanners consistently shows that none provide 100% virus detection. The best ones provided as high as 99.6% detection, while the lowest provide only 81.8% in tests conducted in February 2010. All virus scanners produce false positive results as well, identifying benign files as malware.
Most popular anti-virus programs are not very effective against new viruses, even those that use non-signature-based methods that should detect new viruses. The reason for this is that the virus designers test their new viruses on the major anti-virus applications to make sure that they are not detected before releasing them into the wild.
|“||It's something that they miss a lot of the time because this type of [ransomware virus] comes from sites that use a polymorphism, which means they basically randomize the file they send you and it gets by well-known antivirus products very easily. I've seen people firsthand getting infected, having all the pop-ups and yet they have antivirus software running and it's not detecting anything. It actually can be pretty hard to get rid of, as well, and you're never really sure if it's really gone. When we see something like that usually we advise to reinstall the operating system or reinstall backups.||”|
The detection of rootkits are a major challenge for anti-virus programs. Rootkits are extremely difficult to detect and if undetected, rootkits have full administrative access to the computer and are invisible to users e.g. a rootkit will not be shown in the list of running processes in the task manager. Rootkits can modify the inner workings of the operating system and tamper with the anti-virus program. If a rootkit hides itself in firmware e.g. the motherboard BIOS, it may never be discovered and could persist even if the operating system is cleanly installed on a reformatted or new hard drive.